1. Field of the Invention
This invention relates to the formation of integrated circuit devices. More particularly it relates to the reduction of channeling and/or diffusion of a boron dopant in an LDD region of a PMOS device by implantation with noble gas ions of a portion of a semiconductor substrate where the P- LDD region will be subsequently formed.
2. Description of the Related Art
In the formation of integrated circuit structures having ever decreasing dimensions, the tolerance for channeling and/or diffusion of doped regions decreases as the dimensions of the semiconductor devices are reduced. Many MOS devices are formed with lightly doped drain (LDD) regions between the drain region and the channel portion of the MOS device to improve the performance of the MOS device. It is, therefore, of particular interest to be able to control the channeling and or/diffusion of the dopant used to form such LDD regions in a semiconductor substrate.
It is known that the presence of implanted noble gas ions, such as argon ions, in a semiconductor substrate, such as a silicon substrate, can have an effect on conventional dopants (boron, phosphorus, and arsenic) in the substrate used to provide certain types of conductivity (e.g., N or P type regions) in the silicon substrate. is also known that the implantation of a single crystal lattice in a semiconductor substrate, such as a silicon substrate, with sufficient dosages of noble gas ions such as argon ions, can have a disruptive effect on the crystal lattice of the substrate. Cullis et al., in "Comparative Study of Annealed Neon-, Argon-, and Krypton-Ion Implantation Damage in Silicon", published in the Journal of Applied Physics 49(10) in October 1978, at pages 5188-5198, reported that silicon layers bombarded with high doses (8.times.10.sup.14 atoms/cm.sup.2) of argon ions at 100 keV followed by annealing at 1000.degree. C. gave complex dislocation entanglements, together with other lattice defects, and stated that the implantation of Ar.sup.+ ions into silicon is known to result in a lattice disorder which is particularly hard to remove by annealing.
Milgram et al. in "Effect of Argon Implantation on the Activation of Boron Implanted in Silicon", published in Applied Physics Letters 42(10) in May of 1983, at pages 878-880 reports that both the electrical activation and diffusion of boron implanted in silicon was inhibited by the prior or subsequent implantation of the boron-doped region of the substrate with argon at a dosage of 1.0.times.10.sup.15 argon ions/cm.sup.2, a dosage level said to be sufficient to produce an amorphous layer.
Delfino et al. in "Epitaxial Regrowth of Silicon Implanted with Argon and Boron", published in Applied Physics Letters 44(6) in March, 1984, at pages 594-596, report that a silicon substrate implanted with a 1.0.times.10.sup.15 ions/cm.sup.2 dosage of argon and a 1.0.times.10.sup.14 ions/cm.sup.2 dosage of boron can be subsequently annealed at 900.degree. C. and further indicate that the combined presence of the boron and argon atoms in the lattice appears to enhance the annealing rate without redistribution of the boron dopant.
Aronowitz, in "Quantum-Chemical Modeling of Boron and Noble Gas Dopants in Silicon", published in the Journal of Applied Physics 54(7) in July, 1983, at pages 3930-3934, observed that when argon and boron were implanted together, both the diffusion and the electrical activation of boron are found to be retarded in the presence of argon, irrespective of whether or not the argon was implanted before or after the boron, and indicates that such results imply that the defects created by the implanted argon may act as centers to attract the boron, or that the argon itself might act to attract the boron.
Aronowitz U.S. Pat. No. 4,689,667 describes the controlling of dopant diffusion and dopant electrical activation by the implantation of noble gas atoms such as argon, implanted at a dosage of 1.times.10.sup.15 argon ions/cm.sup.2, and shows that the combination of argon and a second dopant can have an interactive effect to control the electrical activation and attenuate the spatial distribution of a first dopant atom.
Aronowitz, in "Interactions Between Interstitial Atoms in Silicon: Arsenic-Argon-Boron and Boron-Argon-Phosphorus", published in the Journal of Applied Physics 63(4) in February, 1988, at pages 1037-1040, states that it is known that regions in silicon with overlapping populations of implanted arsenic and argon display reduced arsenic diffusion and diminished electrical activity. This is said to have been used by others as a mechanism to reduce electrical fields in the vicinity of the drain in a short-channel MOS device. The author goes on to state that when argon and boron are implanted at energies such that their peak concentrations collide, then both reduced boron electrical activity and mutually retarded argon and boron diffusion patterns are observed.
Thus, the interaction of implanted noble gas ions and implanted dopants in single crystal semiconductor substrates is well known, including the damage which occurs to a silicon substrate, the retardation of diffusion of dopant atoms in a semiconductor substrate in the presence of the noble gas atoms such as argon, and the negative effect on electrical activation of the dopant, although the semiconductor substrate damage appears to be repairable upon subsequent annealing, and the effect of the noble gas ions such as argon ions on subsequent electrical activation seems to be less with boron than with N-type dopants.
However, it would be desirable to control both the diffusion and channeling of a dopant in a semiconductor substrate, such as a single crystal silicon substrate, without disrupting (amorphizing) the single crystal structure of the substrate.